Preparation And Properties Of Polycrystalline And Single-crystal Diamond By MPCVD

Diamond is an important semiconduct material which has many applications due to its excellent properties.Diamond film or single-crystal diamond preparied by MPCVD method has advantage than other method.In this article,high-quality transparent self-standing polycrystalline diamond film and large size single-crystal diamond were synthesized using MPCVD,and its growth characteristics were analyzed.The thesis includes two parts:Part one:several parameters that affect the growth of polycrystalline diamond were analyed,especially on the influence of nitrogen and oxygen on the growth characteristics of polycrystalline diamond.Hight quantity and transparent diamond films were prepared with the most optimize condition.1,In the MPCVD deposition process,the carbon concentration(methane concentration) greatly influence on the growth characteristics of diamond films.The growth rate of the film increased as the methane concentrations increaes,but the quality decline.2,Microwave power is another factor that affect the film growth characteristics. it directly affect the color,shape and energy density of the plasma glow,thus affecting the composition of the various radicals in reaction tatol gas.The growth rate increases as the power increase until to 4.5 kW and then kept nearly constant.3,By analysing the role of nitrogen and oxygen,we found a small amount addition of oxygen etched away non-diamond carbon phase more effectively in favor of promoting the growth rate and quality of single-crystal diamond.Similarly,proper nitrogen addition will increase the growth rate of diamond films and the prefer face is (100) crystal face,but would reduce the quality of diamond simultaneity.4,Transparent self-standing diamond films with thickness of 600μm were acheived with the optimize deposition conditions.Part two:The high rate growth process and optical properties of homoepitaxial CVD single-crystalline diamonds have been studied as well.1,The effect of variation of holders on the growth of single-crystal diamond is discussed.2,High rate growth(80-100μm/h) of homoepitaxial CVD single-crystalline diamonds has been achieved by adding a small amount of nitrogen in the reaction gases.3,The disappearance of void defect on the top surface of single-crystalline diamonds is discussed to be related to a filling-in mechanism.4,We also analysed the impact of oxygen and nitrogen on single-crystal diamond growth by addition of different proportion of oxygen and nitrogen,it demonstrsted that a small amount of oxygen could promote the growth rate and quality of single-crystal diamond,but too much oxygen would hinder its growth rate;similarly, proper nitrogen addition not only promote the single-crystal diamond(100) the growth but also increase its growth rate,but excessive will increase the generation of non-diamond phase and decrease the quality5,The results of PL spectrum showed that the nitrogen concentration is spatially inhomogeneous either on the top surface or in the bulk of the as-grown single-crystalline diamonds.The nitrogen concentration is higher in center than edge on the surface while saturation at a depth with increase in thickness from the topsurface.6,The presence of N-distribution is attributed to the N-diffusion,resulting from the local growth temperatures changed during the high-rate deposition process.In addition,the nitrogen-vacancy centers play a crucial role in N-diffusion through the growing crystal.